1. Technical Field
The present invention relates to a projector for displaying images on a projection surface.
2. Related Art
When displaying an image with a rectangular image area on a projection surface such as a screen using a projector, the image area of the image (hereinafter also referred to as a “projected image”) displayed on the projection surface might be distorted into a trapezoidal shape depending on a relative positional relationship between the projector and the projection surface. On such an occasion, there is used a keystone correction for correcting the distortion (hereinafter also referred to as “keystone distortion”) of the projected image (see, e.g., JP-A-2006-54824).
For example, in the case in which the image (hereinafter also referred to as a “corrected image”) on which the keystone correction process is executed is displayed on the projection surface, the user might move the projector to change the position where the image is displayed. FIGS. 9A and 9B are explanatory diagrams showing how the user moves the projector thereby changing the position where the image is displayed. FIG. 9A shows the state in which the projector 100p of the related art is installed so as to be tilted an angle θ1 upward from the horizontal. FIG. 9B shows the state in which the projector 100p is installed horizontally. As shown in FIGS. 9A and 9B, the image is projected on a wall surface. The user at first displays the image on the wall surface at the position shown in FIG. 9A, and then changes the tilt of the projector 100p so as to display the image on the lower side of the position shown in FIG. 9A. It should be noted that here the position of the image displayed on the wall surface is assumed not to move in a lateral direction.
FIGS. 10A1 through 10A4, and 10B1 through 10B4 are explanatory diagrams conceptually showing the displayed image in the case in which the position of the projector is moved as shown in FIGS. 9A and 9B. FIGS. 10A1 through 10A4 show a liquid crystal panel 154 provided to the projector 100p. In the entire area of the liquid crystal panel, an image light generation area IG, which generates the image light representing the image, is indicated by hatching with oblique lines. It should be noted that the image light generation area on which the keystone correction process is not executed is denoted as IG0, the image light generation area on which the keystone correction process at the projector position shown in FIG. 9A (also referred to as a keystone correction 1) is executed is denoted as IG1, and the image light generation area on which the keystone correction process at the projector position shown in FIG. 9B (also referred to as a keystone correction 2) is executed is denoted as IG2.
FIGS. 10B1 through 10B4 show an image display area PIG as an area of the wall surface where the image is displayed. FIGS. 10B1 through 10B4 show the displayed image viewed from the user located right in front of the wall (FIGS. 9A and 9B). A panel display area PA, which is the entire area of the liquid crystal panel 154, is illustrated with broken lines. The image display area PIG where the image represented by the image light modulated by the liquid crystal panel 154 is indicated by hatching with oblique lines. It should be noted that the image display area before executing the keystone correction 1 is denoted as PIG0, the image display area after executing the keystone correction 1 at the projector position shown in FIG. 9A is denoted as PIG1, the image display area before executing the keystone correction 2 at the projector position shown in FIG. 9B is denoted as PIG2, the image display area after executing the keystone correction 2 is denoted as PIG3.
In the case in which the projector 100p is installed so as to be tilted the angle θ1 upward from the horizontal as shown in FIG. 9A, the image light generation area IG0 is identical to the entire area of the liquid crystal panel 154 in the state in which the keystone correction process is not executed (FIG. 10A1). On this occasion, the image display area PIG0 is distorted to have a trapezoidal shape (FIG. 10B1).
In FIGS. 10A1 through 10B4, the center PC of the liquid crystal panel 154 and the panel display area PA is denoted as a rhombic symbol, and the center IC of the image light generation area IG and the image display area PIG is denoted as a black circular symbol. In the present embodiment, an intersection between the line bisecting the height of the image light generation area IG and the line bisecting the width thereof is defined as the center IC of the image light generation area IG. The same is applied to the center IC of the image display area PIG. The reason therefor is that when viewing the projected image, the user often recognizes the vicinity of the intersection between the line bisecting the height of the projected image and the line bisecting the width thereof as the center of the projected image. Incidentally, the center PC of the panel display area PA is defined as the center of the figure of the panel display area PA. For example, in the case in which the panel display area PA forms a trapezoidal shape, the intersection of the diagonal lines thereof corresponds to the center PC of the panel display area PA.
As shown in FIG. 10A2, when the keystone correction process is executed, the image light generation area IG1 (FIG. 10A2) is formed by distorting the image light generation area IG0 (FIG. 10A1) of the liquid crystal panel 154 in the counter direction with respect to the image displayed on the projection surface. When executing the keystone correction 1 in such a manner, the position is often shifted between the center PC (rhombic symbol) of the liquid crystal panel 154 and the center IC (black circular symbol) of the image light generation area IG1 (FIG. 10A2).
Subsequently, in order for displaying the image on the lower side (FIG. 95) of the display position of the image shown in FIG. 9A, the user moves the projector 100p, and installs the projector 100p horizontally. On this occasion, since a keystone correction amount (parameter) of the keystone correction process is not changed, as shown in FIG. 10A3, the shape of the image light generation area IG1 remains as shown in FIG. 10A2. At the position shown in FIG. 9B, the projector 100p is installed horizontally, and is opposed right to the wall surface.
Therefore, the panel display area PA2 becomes to have a rectangular shape, which is the same as the shape of the liquid crystal panel 154 (FIG. 10B3). When executing the keystone correction process (described as the keystone correction 2 in FIG. 10A3) again in the state in which the projector 100p is installed horizontally (FIG. 95), the image display area PIG2 becomes identical to the entire area of the liquid crystal panel 154 (FIG. 10A4). Therefore, the image with the rectangular image display area PIG2 is displayed on the wall surface (FIG. 10B4).
The user supposes that when the keystone correction 2 is executed after installing the projector 100p horizontally, the image display area FIG corrected to have a rectangular shape centered on the center IC of the image display area PIG1 shown in FIG. 10B3 is displayed. The image display area FIG supposed by the user is illustrated with dashed lines in FIG. 10B4. The center SIC of the image display area EIG is indicated by a black rectangular symbol. The position of the center SIC (FIG. 10B4) of the image display area EIG is identical to the center IC (FIG. 10B3) of the image display area PIG1.
However, the center IC of the image display area PIG after executing the keystone correction 2 becomes identical to the center PC of the panel display area PA2, but not identical to the center EIC of the image display area EIG (FIG. 10B4). In other words, the image display area PIG2 is formed at a position different from the position supposed by the user (FIG. 10B4).